Congestive heart failure (CHF) is a progressive and debilitating disease that affects an estimated 23 million people worldwide. In the U.S., for instance, approximately 7.5 million people have congestive heart failure (CHF), and more than 670,000 new cases are typically diagnosed each year. The treatment of this volume of patients has been reported as costing the healthcare industry almost $35 billion annually.
Treatment strategies for patients with congestive heart failure typically consist of conventional pharmacologic therapy, which is used for purposes of slowing progression of the disease and to ease symptoms. In advanced stages of the disease, treatment may consist of continuous intravenous inotropic support and subsequent heart transplantation, when qualifications are satisfied and a matched donor heart is located.
While heart transplantation is a viable therapeutic when patients qualify, there is a limited number of donor hearts. For instance, in the U.S. in a given year, over about 3000 patients may be on a waiting list for heart transplants, but only approximately 2200 patients will likely receive a transplant. Accordingly, in excess of 15% of patients on the donor waiting list will likely succumb to the disease due primarily to the lack of a sufficient number of donor hearts. This limitation and the increasing need for biventricular support have necessitated the development of therapeutic alternatives, such as mechanical circulatory support systems, including total artificial hearts (TAHs) and ventricular assist devices (VADs) for use as destination therapy or bridge-to-transplantation.
Blood is in and of itself a tissue with both cellular and fluid components. Cells are suspended in a liquid referred to as plasma. When a blood pump or the like of a TAH or VAD is used to add energy to blood, it is extremely important not to cause damage to red blood cells in particular, which carry oxygen in the body.
TAHs may be designed as pulsatile or continuous flow devices for supporting the systemic and pulmonary circulations. Generally, pulsatile pumps or positive displacement pumps may experience critical failures due to moving parts, namely mechanical valves and flexing membranes. High shear stresses and regions of stagnant flow have led to issues with clot formation inside such devices. Further, high shear stresses as the result of mechanical valves can cause hemolysis where red blood cells are split open releasing hemoglobin. Hemolysis activates platelets in the vicinity leading to thrombus formation or thrombogenesis.
Clinical research appears to indicate that pulsatility in the systemic and pulmonary circulations is not critical for physiologic function. Accordingly, continuous flow pumps with impellers suspended by magnetic bearings are believed to be better able to reduce and prevent regions of stagnant flow and high shear stress through limited contact with the blood. However, thrombus formation or thrombogenesis can occur as the result of poor wash-out of blood contacting surfaces of a TAH leading to stagnant blood that activates platelets causing red blood cells to combine together to form a thrombus. Thus, it is clear that blood cell trauma is a very serious complication of mechanical circulatory devices.
Accordingly, there continues to be a need for the further design and development of TAHs for patients suffering from end stage heart disease. A device designed to reduce complications typically associated with current devices as discussed above and that may be provided as a smaller and more effective TAH capable of suiting a wider patient population may result in the saving of thousands of lives annually. Improvements with respect to biocompatibility of device designs and materials are also desired for purposes of decreasing hemorrhagic and thromboembolic complications, and systems to power implanted driving units, which are fully operational without interruption of skin barriers, are desired to mitigate the risk of infections. Further, a TAH that is more compact and effective for use in smaller adults and children and that have fewer mechanical components to reduce wear and risk of failure is desired.